1. Field of the Invention
The present invention relates to disk drives; more particularly, to disk drives which have increased storage capacity and reduced size, weight and power consumption.
2. Description of the Related Art
The technology relating to data storage is following a continuing trend towards increased storage capacity, reduced data storage device weight and size, and reduced power consumption. Factors motivating these trends include the increasing use of portable or lap-top computers.
Reducing the size of disk drives has been balanced against the corresponding reduction in storage capacity caused by a reduction in the area of the storage medium. The sole attempt to introduce a disk drive smaller than the 3 1/2" form factor is a drive announced by Prairie Tek having a disk with a diameter of 65 mm, which is 30 mm less than the diameter of the disks in the 3 1/2" disk drives.
Disk drive manufacturers and computer manufacturers usually establish standards for vibration and shook resistance for hard disk drives or (disk files) for data storage. Among the criteria imposed on hard disk drives are vibration resistance, compactness, low weight, low power, and ease of manufacture--particularly reduced part count. All of these criteria are usually important to a computer manufacturer selecting a disk drive for use in a specific computer or for a specific type of application. The standards may be more stringent for disk drives intended for use in portable or lap-top computers or other harsh environments. Vibration and impact acceptance evaluations may be conducted by placing the drive being evaluated on a vibration table and subjecting the drive to vibrations of varying frequency and amplitude while the drive is operating. The performance of the drive is monitored to determine the frequency and amplitude of the applied vibrations which cause errors in seeking and/or track following. Seek and/or track following errors often result in "hesitations" in reading and/or writing data, and disk drives which are sensitive to applied vibrations of too low a frequency or amplitude may fail acceptance evaluations.
One effect of vibrations applied to a disk drive, and one cause of errors in seeking and/or track following is mechanical off-tracking, i.e., an unintended physical movement of the heads with respect to the disk(s). Mechanical off-tracking may be caused by movements of various structural components on the disk drive with respect to the disk.
Conventional disk drives have been fabricated of dense, heavy materials to provide the structural rigidity necessary to prevent thermal gradients and other physical stresses from causing mechanical off-tracking. The use of heavy materials such as metals has made it difficult to reduce the weight of the disk drive. The use of metals, particularly aluminum, to fabricate the support structure of a disk drive flows the coefficient of thermal expansion of the support structure to be matched to that of many of the internal components of the drive which are also usually fabricated of aluminum.
Disk drive systems utilizing closed-looped head positioning control systems rely on servo data stored on the rotating disks as the source of data track positioning feedback information. One approach to providing such servo information is to dedicate an entire disk surface and corresponding servo read data channel for the near-continuous sourcing and capture of positioning information. However, dedication of an entire disk surface and the need to provide special servo control read circuitry results in a significant increase in the cost per unit data of the disk drive control system and disk drive as a whole.
Conventional hard disk drives often incorporate a device for parking the head(s) of the drive. As used in this patent, the terms "park" and "parking" refer to maintaining the position of the head(s) over a selected portion (usually a "landing zone" at the inside or outside diameter) of the disk (or disks) by latching the actuator which supports the head(s). Many parking devices park the head(s) by physically engaging (latching) the actuator, and the terms "latched" and "unlatched" respectively refer to the engagement and disengagement of the parking device and the actuator. Physical shocks experienced during shipping or other non-operational movements of a disk drive may cause the head to "slap" against the disk, possibly causing a loss of data if the head slaps against a data-carrying portion of the disk. Parking the head assures that the head will land on the landing zone--i.e., a non-data storage portion of the disk--and will be held in a position over the landing zone during the power down period.
Electromagnetic parking devices require electrical power to release the parking device during operation of the disk drive. This use of electrical power is detrimental to the life of the batteries in a portable computer. Purely magnetic parking devices park the actuator by the attraction of and direct contact between a magnetically permeable portion of the actuator and a magnet. The primary drawback of a magnetic latch of this type is that during operation of the disk drive the rotational movement of the actuator is adversely affected by the attraction of the magnetically permeable portion of the actuator and the magnet, thereby creating problems with the track following and seek functions. Further, an extremely large force is required to release the actuator from the magnet.